January 10, 1896.] 



SCIENCE. 



71 



We are pleased to note that for the first time 

 in any somewhat general treatise of botany the 

 Hepaticse have received something like their 

 proper treatment, and their representative posi- 

 tion as a highly important group ft-om the stand- 

 point of phylogeny is clearly stated at the outset 

 and strikingly developed through the work. A 

 fair estimate of their differentiation and highly 

 probable antiquity is also well set forth. 



Dr. Campbell regards the lowest Metzgeria- 

 cese, like Sphserocarpus, as the simplest plants 

 of the entire group and considers that the other 

 groups of the Hepaticse were differentiated from 

 the ancestors of some plant of this character 

 before the development of the sporophyte had 

 . advanced so far as in present forms of that 

 genus. He sets forth a most excellent answer 

 to the remarkable position of Goebel regarding 

 the status of Buxbaumia and contributes several 

 new points bearing on the interrelationships of 

 the various groups of the true mosses. 



In classification Dr. Campbell does not depart 

 widely from arrangements that have heretofore 

 been set forth, in the Hepaticse, for instance, 

 following the lead of Schiifner. The position 

 of Isoetes as the possible ancestor of the Angio- 

 sperms is perhaps the most divergent point 

 presented in the classification. 



Comparison of the work of others is well 

 made, and wherever criticism occurs it is always 

 in the friendly, urbane spirit that ought always 

 to characterize workers in science; where con- 

 clusions are stated, they are couched in pointed 

 and forcible language but never dogmatically. 

 Altogether the work is a valuable contribution 

 and will stand comparison with the best work 

 of the kind that has been done anywhere. 



L. M. Underwood. 



Molecules and the Molecular Theory of Matter, by 



A. D. RiSTEEN, S. B. Giun & Co. Octavo, 



pp. 213. 



This is an excellent resume of the present 

 state of our knowledge of the molecular theory, 

 excluding most of the more difiicult mathemati- 

 cal discussions, and including the principal con- 

 clusions of Clausius, Kelvin, Boltzmann, Max- 

 well and many others who have cultivated this 

 department of physical science. 



After some general considerations involving 



a presentation of the hypothesis of molecules 

 and a definition of what is meant by a molecule, 

 together with a brief statement of the assumed 

 molecular constitution of solids, liquids and 

 gases, the kinetic theory of gases is seriously 

 taken up. The fundamental assumptions of 

 the theory are discussed, Maxwell's Theorem 

 is proved and the statistical method of treat- 

 ment illustrated. The results of the kinetic 

 theory are compared with the results of observa- 

 tion, and the chapter includes an examination 

 of high vacua phenomena, the radiometer and 

 other of Crookes' experiments. 



The chapter on the Molecular Theory of 

 Liquids includes, among other things, a fairly 

 complete elementary study of surface tension 

 and the phenomena of films. Chapter IV. is 

 given to the Molecular Theory of Solids, con- 

 cerning which there is really little known, but 

 interesting studies of the phenomena of solution, 

 diffusion, crystallization, etc., are here given. 

 The concluding chaptere on the Molecular 

 Magnitude and the Constitution of Molecules 

 are important and well done. The principal 

 methods for determining molecular dimensions 

 are gone into pretty thoroughly and the more 

 recent hypothesis in regard to the constitution 

 of the ether and the nature of matter are pre- 

 sented with great clearness and some fullness. 



Among a few unimportant criticisms of the 

 book that suggest themselves may be mentioned 

 the holding on to the ' lecture ' form of presen- 

 tation. The foundation of the work was a lec- 

 ture given by the author before the Washburn 

 Engineering Society of the Worcester Polytech- 

 nic Institute, but it has been so expanded, and 

 so much additional material has been supplied 

 that it exceeds the limits of several lectures. 

 As a large part of the new material is not in the 

 lecture form and as little is gained by retaining 

 it anj'how, it is to be regretted that the author 

 did not reject it in the beginning. 



As an echo of the discussion which occurred 

 at the recent meeting at Springfield of the So- 

 ciety for the Promotion of Engineering Educa- 

 tion, it may be well to note that on one or two 

 pages this book illustrates the fatal results which 

 are almost sure to follow the use of the formula 

 W:=mg, in the good old orthodox way. The 

 author is lucky, however, in having apparently 



